Mark King writes:
Myself and some friends came across hundreds of these bioluminescent jellies on Rossnowlagh beach, Co Donegal at low tide last night [Saturday]. When disturbed, they glow bright blue. From what I can gather, they’re rarely seen here and seemed to be gathered almost entirely in front of a hotel – the only lit up part of the beach. Maybe some of your readers can help shed some light (sorry…) as to why?